The proposed study will be a national collaborative randomized clinical trial of photocoagulation treatment for central retinal vein occlusion. The study will be conducted at 8-10 clinical centers with the Coordinating Center at Scott and White Hospital (Texas A&M University), and the Reading Center at Bascom Palmer Eye Institute (University of Miami). This application is for a particular center. Patients will be entered into four study groups: Non-perfused (Group N), Macular Edema (Group M), Perfused (Group P), and Indeterminant (Group I). Eyes in the first two groups will be randomly assigned to photocoagulation and a control group respectively. Patients in the latter two groups will be followed for natural history and for possible later entry into the randomized study. Estimated recruitment is 240 for Group N, 160 for Group I, and 400 for Group P. Approximately 50% of these patients will also qualify for Group M. Patients will be recruited for the first three years of this five year study; all patients will be followed until study termination. The study is designed to provide information concerning the efficacy of photocoagulation in preventing neovascular glaucoma in eyes with central retinal vein occlusion and retinal non- perfusion and the usefulness of photocoagulation in preserving visual acuity in eyes with central vein occlusion and macular edema. Data will be collected at baseline and at each follow up visit and forwarded to the Coordinating Center for analysis. Photographs will be reviewed at the Reading Center to determine eligibility and adequacy of treatment. A Data Monitoring Committee will review interim results every six months.